Silicon-based anti-herbivore defense in tropical tree seedlings

Area of Science:

• Ecology
• Plant Science
• Chemical Ecology

Background:

• Silicon (Si) is known to deter insect herbivores in grasses, with defenses sometimes induced by herbivory.
• Tropical trees accumulate Si, but its role in constitutive and inducible anti-herbivore defense is unknown.
• Herbivory significantly impacts tropical tree seedling mortality and niche differentiation.

Purpose of the Study:

• To investigate whether silicon provides constitutive and inducible herbivory defense in tropical tree species.
• To determine the species-specific effects of soil silicon availability and simulated herbivory on plant defense.

Main Methods:

• Seedlings of eight tropical tree species were grown under varying soil silicon concentrations (-Si/+Si) and simulated herbivory (-H/+H).
• Simulated herbivory involved clipping and methyl jasmonate application.
• Multiple-choice feeding trials with generalist caterpillars (Spodoptera frugiperda) were conducted, followed by leaf damage assessment.

Main Results:

• Three species exhibited significantly reduced leaf damage under high Si conditions, indicating constitutive Si-based defense.
• Effects of Si on herbivore damage varied significantly across species; one species showed increased damage with higher Si.
• Simulated herbivory did not consistently induce defenses and, in some cases, increased damage or reduced Si concentrations.

Conclusions:

• Constitutive silicon-based defense is present in some tropical tree species, with effectiveness varying by species and soil Si levels.
• Silicon-based defenses in tropical trees appear largely non-inducible by herbivory.
• Species-specific Si-based defenses and soil Si availability can significantly influence tropical tree regeneration and performance.